Ribavirin (1-β-D-ribofuranosyl-1,2,4-triazole-3-carboxamide) is a nucleoside analog that has demonstrated efficacy in treating viral diseases both as monotherapy (respiratory syncytial virus, Hall, C. B.; McBride, J. T.; Walsh, E. E.; Bell, D. M.; Gala, C. L.; Hildreth, S.; Ten Eyck, L. G.; W. J. Hall. Aerosolized ribavirin treatment of infants with respiratory syncytial viral infection. N. Engl. J. Med. 1983, 308, 1443-1447), and in combination therapy with interferon-alpha (hepatitis C virus, Reichard, O.; Norkrans, G.; Fryden, A.; Braconier, J-H.; Sonnerborg, A.; Weiland, O. Randomized, double blind, placebo controlled trial of interferon alpha 2B with and without ribavirin for chronic hepatitis C. Lancet 1998, 351, 83-87). Recently reported studies indicate that the in vivo utility of ribavirin can result not only from direct inhibition of viral replication, but also from its ability to enhance T cell-mediated immunity (Hultgren, C.; Milich, D. R.; Weiland, O.; Sallberg, M. The antiviral compound ribavirin modulates the T helper Type1/Type2 subset balance in hepatitis B and C virus-specific immune responses. J. Gen. Virol. 1998, 79, 2381-2391; Ning, Q.; Brown, D.; Parodo, J.; Cattral, M.; Fung, L.; Gorczynski, R.; Cole, E., Fung, L.; Ding, J. W.; Liu, M. F.; Rotstein, O.; Phillips, M. J.; Levy, G. Ribavirin inhibits viral-induced macrophage production of tumor necrosis factor, interleukin-1, procoagulant activity fgl2 prothrombinase and preserves Th1 cytokine production but inhibits Th2 cytokine response. J. Immunol. 1998, 160, 3487-3493; Martin, M. J.; Navas, S.; Quiroga, J. A.; Pardo, M.; Carreno, V. Effects of the ribavirin-interferon alpha combination on cultured peripheral blood mononuclear cells from chronic hepatitis C patients. Cytokine 1998, 79, 2381-2391. This immunomodulatory effect of ribavirin is demonstrable in vitro by measuring the levels of Type 1 cytokines produced by activated T cells from both humans and mice (Tam, R. C.; Pai, B.; Bard, J.; Lim, C.; Averett, D. R.; Phan, U. T.; Milovanovic, T. Ribavirin polarizes human T cell responses towards a Type 1 cytokine profile. J. Hepatol. 1999, 30, 376-382), and by other measures. The induction of a Type 1 cytokine bias by ribavirin is functionally significant in vivo in murine systems (Tam, R. C.; Lim, C.; Bard, J.; Pai, B. Contact hypersensitivity responses following ribavirin treatment in vivo are influenced by Type 1 cytokine polarization, regulation of IL-10 expression and costimulatory signaling. J. Immunol. 1999, 163, 3709-3717).
Mammalian immune systems contain two major classes of lymphocytes: B lymphocytes (B cells), which originate in the bone marrow; and T lymphocytes (T cells) that originate in the thymus. B cells are largely responsible for humoral immunity (i.e., antibody production), while T cells are largely responsible for cell-mediated immunity.
T cells are generally considered to fall into two subclasses, helper T cells and cytotoxic T cells. Helper T cells activate other lymphocytes, including B cells and cytotoxic T cells, and macrophages, by releasing soluble protein mediators called cytokines that are involved in cell-mediated immunity. As used herein, lymphokines are a subset of cytokines.
Helper T cells are also generally considered to fall into two subclasses, Type 1 and Type 2. Type 1 cells produce interleukin 2 (IL-2), tumor necrosis factor (TNFα) and interferon gamma (IFNγ), and are responsible primarily for cell-mediated immunity such as delayed type hypersensitivity and antiviral immunity. In contrast, Type 2 cells produce interleukins, IL-4, IL-5, IL-6, IL-9, IL-10 and IL-13, and are primarily involved in assisting humoral immune responses such as those seen in response to allergens, e.g. IgE and IgG4 antibody isotype switching (Mosmann, 1989, Annu Rev Immunol, 7:145-173).
As used herein, the terms Type 1 and Type 2 “responses” are meant to include the entire range of effects resulting from induction of Type 1 and Type 2 lymphocytes, respectively. Among other things, such responses include variation in production of the corresponding cytokines through transcription, translation, secretion and possibly other mechanisms, increased proliferation of the corresponding lymphocytes, and other effects associated with increased production of cytokines, including motility effects.
Previous applications (Ser. Nos. 09/462,714, 09/291,097, 09/291,093, 09/471,513, 60/164,365, 60/164,366, 60/172,097, 60/175,111), each of which is incorporated herein by reference, relate to aspects of our recent discoveries involving the effect of various nucleosides (which are defined herein to include derivatives and analogs of native nucleosides) on selectively modulating lymphocyte responses relative to each other. Among other things, we have shown that either of Type 1 and Type 2 responses can be selectively suppressed while the other is either induced or left relatively unaffected, and either of Type 1 or Type 2 responses can be selectively induced while the other is either suppressed or left relatively unaffected. We have also discovered the surprising fact that some nucleosides effective in selectively modulating Type 1 and Type 2 responses relative to one another tend to have a bimodal effect. Among other things, some nucleosides that tend to generally suppress or induce both Type 1 and Type 2 activity at a relatively higher dose tend to selectively modulate Type 1 and Type 2 relative to each other at relatively lower doses.
Viramidine™ (1-β-D-ribofuranosyl-1,2,4-triazole-3-carboxamidine hydrochloride) has been shown active in ten different viruses that is comparable to Ribavirin. (J. T. Witkowski, R. K. Robins, G. P. Khare, R. W. Sidwell, J. Med. Chem., 16, 935-937, 1973; R. W. Sidwell, J. H. Huffman, D. L. Barnard, D. Y. Pifat, Antiviral Research, 10, 193-208, 1988; B. Gabrielsen, M. J. Phelan, L. Barthel-Rosa, C. See, J. W. Huggins, D. F. Kefauver, T. P. Monath, M. A. Ussery, G. N. Chmurny, E. M. Schubert, K. Upadhya, C. Kwong, D. A. Carter, J. A. Secrist III, J. J. Kirsi, W. M. Shannon, R. W. Sidwell, G. D. Kini, R. K. Robins, J. Med. Chem., 35, 3231-3238, 1992). In addition, Viramidine™ like Ribavirin is an inhibitor of IMP dehydrogenease (R. C. Willis, R. K. Robins, J. E. Seegmiller, Molecular Pharmacology, 18, 287-295, 1980). Furthermore, preliminary toxicology studies suggests that Viramidine™ is less toxic than ribavirin (D. Y. Pifat, R. W. Sidwell, P. G. Canonico, Antiviral Research, 9, 136, 1988). Also, recent studies at our lab (R. Tam, K. Ramasamy, ICN Pharmaceuticcals, Inc., unpublished results, 1999) revealed that Viramidine™ and ribavirin exhibited similar immunomodulatory properties. These results coupled with low bioavailability and the toxicity associated with ribavirin prompt us not only to develop Viramidine™ for other viral diseases but also to prepare other derivatives of Virainidine™, including the synthesis of prodrugs of Viramidine™, and screen them as potential antiviral agents.
The effect of other nucleoside analog compounds on selectively modulating lymphocyte responses relative to each other has not been previously studied or documented. We have discovered that the bimodal effect, or selective modulation of Type 1 and Type 2 responses relative to one another, also occurs after administration of other nucleoside analog compounds, such as pro-drug forms of the compounds.
There are many barriers to overcome in developing biologically active compounds into clinically useful agents. Many potent biologically active compounds never become clinically useful agents because of their undesirable biopharmaceutical properties which include low bioavailability due to low permeability through biological barriers, such as the blood brain barrier (BBB) and the intestinal barrier. Although many factors affect the bioavailability of a drug, the undesirable physicochemical properties (e.g., charge, lipophilicity, hydrogen bonding potential, size) of many drugs is probably one of the most commonly encountered factors that hinder the permeation of drugs through biological barriers. Therefore, optimization of the physicochemical characteristics (charge, lipophilicity, hydrogen bonding potential, size) of a drug is probably the most likely general strategy to facilitate the transport of drugs through such membrane barriers.
To optimize the physicochemical properties of drugs, one possible strategy is that of prodrugs. (H. Bulidgaard, Design of Prodrugs, Elsevier, Amsterdam, 1985; N. Bodor, L. Prolkai, W. M. Wu, H. Farag, S. Jonalagadda, M. Kawamura, J. Simpkins, Science, 257, 1698-1700, 1992; H. E. Taylor, K. B. Sloan, J. Pharm. Sci, 87, 5-20, 1998). The term prodrug is used to describe an agent, which must undergo chemical or enzymatic transformation to the active or parent drug after administration, so that the metabolic product or parent drug can subsequently exhibit the desired pharmacological response. By derivatizing certain polar functional groups in small organic molecules transiently and bioreversibly, the undesirable physicochemical characteristics (e.g., charge, hydrogen bonding potential) of these groups have been “masked” without permanently altering the pharmacological properties of the molecules. This strategy has been very successfully used in cases where the prodrug derivatization involves converting a carboxyl or a hydroxyl functional group into an ester, which can be readily hydrolyzed in vivo either chemically, or enzymatically. The promising prodrug concept, we anticipate that the introduction of other moieties in the parent drug would increase the bioavailabilty, adsorption and antiviral effects.
Despite the existence of as-yet undefined mechanisms, we have discovered that enormous potential benefits can be derived from selective modulation of Type 1 and Type 2 responses relative to each other. We have concluded, for example, that specific modulation of Type 1 relative to Type 2 can be useful in treating a wide variety of conditions and diseases, ranging from infections, infestations, tumors and hypersensitivities to autoimmune diseases.
These discoveries are especially significant because modern treatment strategies for many of the above-listed diseases have limited effectiveness, significant side effects, or both. Treatment of autoimmune disease, for example, is frequently limited to palliative measures, removal of toxic antibodies (as in myasthenia gravis), and administration of hazardous drugs including corticosteroids, chloroquine derivatives, and antimetabolic or antitumor drugs, and drugs such as cyclosporines that target immune system cells.